A lens barrel for holding a shooting lens of a camera and so on, in a state of being attached to a camera body, or in a state of not being attached to the camera body as a lens barrel for a single-lens reflex camera, often receives a great shock when dropped mistakenly or hit by an object.
There are various systems for a lens drive mechanism of the lens barrel. One of the various systems adopted in the lens drive mechanism is a so-called Bayonet connection, in which members in a cylindrical shape are connected by fitting a projection to a cutout and a groove in a circumferential direction, and move relatively to each other. In a case of using the lens barrel adopted in the Bayonet connection, and in a case where the projection is placed in a part which is mechanistically low in strength of a member in the cylindrical shape, when the lens barrel receives a great shock as described above, the member in the cylindrical shape may be deformed and the Bayonet connection may come off. Therefore, there are problems such that the lens barrel does not move smoothly, or does not even move at all.
The reasons for occurrence of such problems described above will be explained more specifically. As for the members in the cylindrical shape, in a linear movement groove formed in one of the members in the cylindrical shape, the projection of the other member is fitted, and the members in the cylindrical shape move relatively to each other in a center axis direction. Additionally, the projection is led into a groove in a circumferential direction extending to the linear movement groove, and the members in the cylindrical shape are connected to each other and rotate relatively to each other around the center axis. A connection where the projection and the groove are fitted together is generally called a “Bayonet connection”. A member with the projection described above often has a clearance groove to a pin to move a lens frame in an optical axis direction when zooming and so on, or a cam groove etc. in a wide range in the circumferential direction. In a case where the clearance groove or the cam groove etc. described above are formed in the member, the strength of the members in the cylindrical shape is degraded. Especially, in the axis direction, in a range where the clearance groove or the cam groove etc. are provided along, the strength tends not to be enough. Therefore, in a case where the projection is provided in this range, when a shock is received, it is easy for the member with the projection to be deformed in a periphery of the projection and it is easy for the projection to come off the groove. That is, it is easy for the Bayonet connection to come off.
It is considered that by enlarging a width of the projection, that is, enlarging a length in the circumferential direction centering on an axis of the members in the cylindrical shape, it is more difficult for the Bayonet connection to come off. However, only enlarging the width of the projection slightly is minimally-effective. If the width of the projection is enlarged greatly, it is more effective in terms of mechanical strength. However, a degree of parallelization of a front side and a back side of the projection in the circumferential direction of the members in the cylindrical shape needs to be processed with high accuracy, therefore it is difficult to manufacture.
There is a Bayonet connection in which a depth of the projection fitting in the groove is deeper, so that it is difficult for the Bayonet connection to come off. Or the members in the cylindrical shape are produced from an aluminum alloy bar by a cutting work and thereby the mechanical strength is enhanced, so that the members in the cylindrical shape are not deformed even if a shock is received. By being structured as described above, it is possible to prevent the Bayonet connection from coming off, even if the members in the cylindrical shape are deformed by the shock, and this also makes it possible to decrease a deformation of the members in the cylindrical shape.
However, in a method in which a fitting part of the Bayonet connection is deeper, a thickness in a radial direction of a member having the fitting part needs to be very thick. Therefore, there is a problem that a diameter of the lens barrel may become larger. And, in a case where a lens barrel is produced from the aluminum alloy bar by the cutting work, the long production time is increased and causing a problem of low productivity. Moreover, compared with members in the cylindrical shape produced from a synthetic resin, there is a problem that a front end slants downward in a state where the members in the cylindrical shape produced from the aluminum alloy bar are extended because of its heavy weight.
As a known example of enhancing the strength of the lens barrel described above, there is Japanese patent publication number 2003-322786. Japanese patent publication number 2003-322786 discloses an invention in which a reinforcing member is used to enhance the strength of the lens barrel.